For a Rational License server ( version v 8.1.2 or above )  to work properly using IPv6 addresses, all systems in an enterprise (including the network hardware and software) must be configured properly to support communication using IPv6 addresses.

Before testing or deploying a Rational Common Licensing-supported or -based application that supports IPv6 or IPv4/IPv6 dual communication, make sure that all systems on the network can communicate successfully. If the license server will run under any of the following operating systems, it can communicate with clients using either IPv4 or IPv6 (as long as the network is configured properly).

• Any supported edition of Windows Vista
• Any supported Linux platform
• Any supported Unix platform

Because these operating systems support dual-layer communication, both IPv4 and IPv6 enabled clients can communicate with an IPv6 license server. Moreover, IPv6 clients can communicate with an IPv4 license server using the IPv4 address, as seen below: 

In the case of a license server hosted on Windows XP or Windows Server 2003 operating systems, there are certain drawbacks because of limited dual-layer support on these operating systems.

• IPv6 enabled clients can communicate with an IPv4 license server running on these operating systems.
• IPv4 clients cannot communicate with a Ipv6 license server running on these operating systems. You might receive “FLEXlm -16 error “ on the client end , refer below tech note to fix the issue: http://www.ibm.com/support/docview.wss?uid=swg21516145

Author: Pankaj Sharma